Process for squeezing water from paper sheet

ABSTRACT

In a paper making machine, following casting of the aqueous pulp suspension onto a moving web and partial drainage of water therefrom to form a wet sheet, water is pressed from the wet sheet by rolls that are characterized by a covering composed of a butadiene acrylonitrile elastomer and a dispersion of hydrophobic fiber strands penetrating through the outer surface of the elastomer. Such rolls have superior release characteristics with respect to the wet sheet.

United States Patent Mitchell, Jr. Aug. 22, 1972 [54] PROCESS FOR SQUEEZING WATER 3,184,828 5/1965 Dames ..29/ l 32 X FROM PAPER SHEET 2,497,696 2/ 1950 Smith ..29/ l 20 X 2 l t t P I i G X [7 or a J c n m 3 2,804,678 9/1957 Rockoff ..29/12| R [73] Assignee: SW lndustrits, lnc., Newton, Mass. 221 Filed: June 1, 1971 F PUBL'CM'ONS [21] pp No: 148,970 Pal??? Magazine, March 1965, Vol. 48, No. 3, Rehud s A fi afion D Materials in Design Engineering" Magazine, Sept. 1957, Pages l43, I44 [60] DIVlSlOn of Ser. No. 83l,l6l, June 6, I969,

Pat. No. 3 639 957 which is a continuation-in- 1 Primary ExarmnerB|lly J. wllhlte part of Ser. No. 606,412, Dec. 30, I966, Pat. No. 3,460,222. Attorney Morse, Altman & Oates 52 us. Cl .100/31, 162/205 [571 [51] Int. Cl. ..B30b 9/02 In a paper making machine, following casting of the 0 aqueous suspension onto a moving web and par- 29/121, 132; 162/205 tial drainage of water therefrom to form a wet sheet, water is pressed from the wet sheet by rolls that are [56] References cued characterized by a covering composed of a butadiene UNITED STATES PATENTS acrylonitrile elastomer and a dispersion of hydrophobic fiber strands penetrating through the outer surface 3,262,840 7/ l966 Hervey 1 62/205 of the elastomer. h rolls have superior release 2,801 i Kusters l X h t i ti p t t th t h t 2,878,778 3/1959 Kusters ..29/l25 X 3,069,304 l2! I962 Fahrbach et al ..29/ I25 X 2 Claim 2 Drawing Figures PROCESS FOR SQUEEZING WATER FROM PAPER SHEET RELATED APPLICATION The present application is a division of Ser. No. 83l,l6l, filed June 6, 1969, now US. Pat. No. 3,639,957, issued Feb. 8, 1972 which in turn, is a continuation-in-part of Ser. No. 606,412, filed Dec. 30, 1966, now US. Pat. No. 3,460,222.

SUMMARY OF THE DISCLOSURE The present invention relates to paper making machines and processes and, more particularly, to enhancement of the release characteristics of rolls in contact with the advancing wet sheet following casting of the aqueous pulp suspension in any of the several different types of paper forming processes. In a typical paper making process, a dilute aqueous slurry of cellulose fibers, which have been produced by grinding wood pulp or the like, first is cast on an endless wire screen through which water is drained, next is advanced into an endless felt, with which it passes between a series of so-called press rolls that squeeze and withdraw water therefrom, next is advanced by itself between a series of press rolls and then is advanced over heated drying cylinders. Difficulties have been encountered as a result of a tendency by fibers of the wet sheet to adhere to the press rolls with which they come in contact.

The primary object of the present invention is to provide improved release characteristics in the elastomeric cover of a press roll for paper sheet formation by the addition of fine fiber strands, ends of which penetrate and protrude through the finished, ground outer surface of the rubber cover. In accordance with the present invention, the elastomeric cover is composed of butadiene acrylonitrile. It is believed that, when the fibers are hydrophobic, the surface tension of a water film on the rubber cover surface is interrupted in such a way as to decrease adhesion of the wet paper filaments to the rubber cover surface as a whole. Other objects of the present invention will in part be obvious and will in part appear hereinafter.

DESCRIPTION OF THE DRAWINGS The invention accordingly comprises the devices and processes possessing the particular components, steps and interrelationships, which are exemplified in the following detailed disclosure, the scope of which will be indicated in the appended claims. For a fuller understanding of the nature and objects of the present invention, reference is to be had to the following description taken in connection with the accompanying drawings, wherein:

FIG. 1 is a distorted cross-sectional, schematic view of a portion of a paper making machine embodying the present invention; and

FIG. 2 is an exaggerated cross-sectional, brokenaway detail view of one of the rolls of the construction of FIG. 1.

SPECIFIC DISCLOSURE In a paper making process involving the present invention, the initial wet sheet 10, is formed by casting a dilute aq ueous slurry of cellulose fibers onto an endless wire screen 11, as is shown in FIG. 1. In accordance with the present invention a so-called lumpbreaker roll 14, which is a press roll embodying the present invention, serves to contact the advancing paper sheet in such a way as to flatten uneven agglomerations of fibers in various portions of the advancing sheet. The sheet next advances onto an endless felt 12. The wet sheet and the felt advance into engagement between a series of press rolls, two of which are shown at 16, 18, after the sheet is separated from screen 11 at 15. Then the wet sheet advances between the nips of a series of press rolls, two of which are shown at 20, 22. When advancing over wire screen 11, on felt l2 and in contact with the various press rolls, generally the moisture content by total weight of the sheet is in excess of 35 percent. The rolls in direct contact with the wet sheet, during this time, are characterized by exceptional release properties in accordance with the present invention. It will be understood that such direct contact rolls may be above and/or below the advancing paper sheet.

As shown in FIG. 2, each of press rolls l4, 16, 20 and/or 22 is shown as having a metal core 24 and an elastomeric veneer 26. The metal core, for example, is in the form of a solid or hollow cylinder composed of metal such as steel or cast iron, or other dimensionally stable material. The veneer contains a matrix of an elastomer 28 and dispersed, randomly distributed fiber strands 30. For best results in accordance with the present invention, the elastomer is. composed of butadiene acrylonitrile. Preferably, the fiber strands are composed of a hydrophobic synthetic polymer, and, most advantageously, are selected from the class consisting of polyesters, polyamides and acrylics. Best results have been achieved with linear polyamides such as polyhexamethylene adipamide. For present purposes, the terrn hydrophobic is applied to a material having a regain of moisture from a bone dry condition of less than 5 percent based on original bone dry weight in an atmosphere having 65 percent relative humidity at F. Preferably, by total weight of the combination, the strands range from 0.5 to [0.0 percent and the elastomeric matrix ranges from 99.5 to percent. For best results, the strands range from A to 5 denier and from one sixty-forth to 2 inches long. Preferably the final composition ranges from 20 to 200 plastometer, :6 inch ball, Pusey and Jones.

EXAMPLE 1 A press roll of the foregoing type was produced as follows. Polyhexamethylene adiparnide strands, 1% denier and 1% inches long, were uniformly dispersed into a mass of uncured butadiene acrylonitrile elastomeric matrix. The resulting dispersion of strands in the matrix was such that, by total weight, the strands were approximately 5 percent and the elastomeric composition was approximately percent. The elastomeric composition was formulated in accordance with typical practice to give a hardness of 35 plastometer, Va inch ball, Pusey and Jones. An iron core, 34 inches in diameter by 184 inches in length, was cleaned and roughened by grit blasting and coated with cement in accordance with well established roll covering techniques. The foregoing formulation was applied in a 1 inch thickness onto the iron core and cured, finished and ground in accordance with well established roll manufacturing techniques. Examination revealed that the ends of the strands penetrated through the ground surface of the chloroprene roll cover. This ground surface was characterized by exceptional release characteristics with respect to wet paper sheet in contact therewith.

EXAMPLE II The foregoing example is repeated with 50, 75 and 100 plastometer, l6 inch ball, Pusey and Jones. with similarly excellent results.

OPERATION AND CONCLUSION The superior release characteristics of the rolls illustrated above are believed to be based, at least in part, on the effect of the free ends of the fiber shreds on the surface tension of a film of water on the roll. These free ends interrupt the uniform wetting of the roll by the wet paper sheet and, thereby, interrupt the uniformity of the surface tension of the layer of water that otherwise would exist on the roll cover. The result is that cellulose fibers from the wet paper sheet, which are swollen with moisture, have a greatly decreased tendency to adhere to the surface of the roll.

Since certain changes may be made in the foregoing disclosure without departing from the scope of the invention involved, it is intended that all matter shown in the accompanying drawing and described in the foregoing specification be interpreted in an illustrative and not in a limiting sense.

What is claimed is:

l. A process for squeezing water from a wet paper sheet, said process comprising the steps of advancing the paper sheet between a pair of pressure surfaces, at least one of said surfaces being constituted by an elastomeric matrix interrupted by hydrophobic, synthetic, polymeric fiber strands which penetrate and protrude through the outer surface of said elastomeric matrix, reducing the surface tension of water in contact with said one of said surfaces by operation of said fiber strands, and freely advancing said paper sheet from contact with said one of said surface, said strands being composed of a hydrophobic synthetic polymer selected from the class consisting of polyesters, polyamides and acrylics, said matrix being butadiene acrylonitrile.

2. The process of claim 1 wherein said strands are composed of a linear polyamide, being approximately within the ranges of /2 to 5 denier in diameter and one sixty-forth to 2 inches in length, said strands by total weight of said veneer ranging approximately from 0.5 to 10 percent and said elastomeric matrix by total weight of said veneer ranging approximately from 99.5 to percent. 

1. A process for squeezing water from a wet paper sheet, said process comprising the steps of advancing the paper sheet between a pair of pressure surfaces, at least one of said surfaces being constituted by an elastomeric matrix interrupted by hydrophobic, synthetic, polymeric fiber strands which penetrate and protrude through the outer surface of said elastomeric matrix, reducing the surface tension of water in contact with said one of said surfaces by operation of said fiber strands, and freely advancing said paper sheet from contact with said one of said surface, said strands being composed of a hydrophobic synthetic polymer selected from the class consisting of polyesters, polyamides and acrylics, said matrix being butadiene acrylonitrile.
 2. The process of claim 1 wherein said strands are composed of a linear polyamide, being approximately within the ranges of 1/2 to 5 denier in diameter and one sixty-forth to 2 inches in length, said strands by total weight of said veneer ranging approximately from 0.5 to 10 percent and said elastomeric matrix by total weight of said veneer ranging approximately from 99.5 to 90 percent. 